The present invention relates to an intake manifold in the intake system of an automobile engine.
Known types of such intake manifolds include the ones disclosed, for example, in Japanese Laid-Open Patent Publication Nos. 9-177624 and 2008-184939.
The intake manifold disclosed in Japanese Laid-Open Patent Publication No. 9-177624 includes a surge tank and a plurality of intake pipes each having an inlet port. The inlet ports of the intake pipes are connected to and protrude into the surge tank. The inlet ports extend in a direction of air flow from the opening of the surge tank, and are arranged along a direction perpendicular to the air flow direction.
The intake manifold disclosed in Japanese Laid-Open Patent Publication No. 2008-184939 also includes a surge tank and a plurality of intake pipes each having an inlet port. The inlet ports of the intake pipes are connected to and protrude into the surge tank. These inlet ports are provided symmetrically on both sides of the opening of the surge tank, and are arranged along the flow direction of air from the surge tank opening.
These types of conventional intake manifold have the following drawbacks.
In the conventional structures disclosed in the above two documents, the inlet ports are arranged inside the surge tank. Thus, when air is drawn into the inlet ports, a great turbulence is likely to be generated about each inlet port. Such turbulence disturbs smooth intake of air, possibly deteriorates the intake performance, and, as a result, lowers the combustion efficiency of the engine.
Particularly, in the configuration disclosed in Japanese Laid-Open Patent Publication No. 2008-184939, a pair of the inlet ports are arranged on either side of the surge tank along the direction of air flow, and open in a direction perpendicular to the flow direction of air. This is likely to generate a great turbulence between adjacent inlet ports, and particularly lowers the intake performance of the inlet ports on the downstream side. As a result, the amount of air drawn into the inlet ports becomes uneven. This not only lowers the combustion efficiency, but also generates irregular vibration as the engine operates.